Study of the ground - to -Very Low Earth Orbit (VLEO) satellite communication link BACHELOR'S DEGREE THESIS Bachelor's degree in Aerospace Vehicles Engineering DOCUMENT 1. REPORT C`andiaMu~nozTard`a Director: Miquel Sureda Anfres Co-Director: Silvia Rodriguez Donaire 10th January 2018 Universitat Polit`ecnicade Catalunya Escola Superior d'Enginyeries Industrial, Aeroespacial i Audiovisual de Terrassa Equipped with his five senses, man explores the universe around him and calls the adventure Science. Edwin Hubble, The Nature of Science, 1954 ii Acknowledgements First of all, I would like to thank Professor Miquel Sureda for guiding me through the development of my Bachelor's degree thesis and for his expert advice when difficulties came up. This study has changed my vision about the space and in part it is thanks to Miquel. Also, I would like to express my gratitude to the Professors Silvia Rodr´ıguez and Daniel Garcia for their advice and to consider me for the DISCOVERER project, in which the present study is included. On the other hand, I would like to express my infinite gratitude to my parents, Anna and Paco, and my brother Biel. They have been supporting me as far back as I can remember and they have not let me down this time neither. I would like to thank Gurinder, too. His patience and immense support helps me every day to look forward. I would not like to finish without thanking my friends. Shearing this experience with them has done it much bearable. Thank you all very much for being with me through this research and let me accomplish my dreams. iii Summary This study is divided in three documents and one DVD which are described below. Document 1. Report The report corresponds to this document and it presents the work that has been done during the development of the study. It is divided into the following parts: • Chapter 1. Introduction: A summary of the aim, scope and objectives is presented beside the justification and the planning of the study. • Chapter 2. State of the art: An explanation of the satellites and types of existing orbits is presented. • Chapter 3. Communication link geometry: The geometry problem between a satellite and a ground station is exposed, together with the equation which calculates the visibility windows time. Also, the Matlab code implemented is explained. • Chapter 4. Communications architecture: A brief introduction of the pro- cess the information collected by the satellites has to follow in order to safely be transmitted to the ground station is presented. • Chapter 5. Results: The different results obtained with the code are exposed. • Chapter 6. Conclusions: With all the information of the thesis, some conclusions about the visibility windows and the implemented code are detailed. • Future work: The possible improvements and the future continuity of the thesis are presented. • Environmental and security impact: An insight of the environmental impact and the security measures of this thesis are commented. • Bibliography: All the references that have been used while developing this work are attached. iv v Document 2. Annexes It contains all the implemented Matlab code. Document 3. Budget In this document, the budget of the implementation of the thesis in a real business is attached. DVD All the files of the study have been burned into a DVD. It includes the electronic docu- ments in PDF format and the images that have been used. Also the Matlab code file has been included. Contents Acknowledgements iii Summary iv List of Figures x List of Tables xi List of abbreviations xii List of abbreviations xiii 1 Introduction 1 1.1 Aim . .1 1.2 Scope . .1 1.3 Requirements . .2 1.4 Justification . .2 1.4.1 Identification of the need . .2 1.4.2 Usefulness of the study . .3 1.5 Study's approach . .3 1.6 Planning . .4 2 Satellites and Orbits 7 2.1 Satellites . .7 2.1.1 CubeSats . 10 2.2 Orbits . 13 2.2.1 Characterization of an orbit . 13 2.3 Types of orbits . 14 2.3.1 Challenges and opportunities of VLEO . 17 3 Communication link geometry 20 3.1 Visibility window . 20 vi vii 3.1.1 Horizon plane . 25 3.1.2 Constants and initial parameters . 27 3.1.3 Satellite - Ground station geometry . 31 3.1.4 Visibility window duration . 37 3.2 Predicting the visibility window: Matlab code . 45 3.2.1 Constants and initial parameters . 45 3.2.2 Calculation of the visibility window duration . 47 4 Communications architecture 58 4.1 Data process . 61 5 Results 67 5.1 Visibility window variation and design data rate . 67 5.2 Comparison with Qbapp . 75 6 Conclusions 78 Future work 81 Environmental impact and security impact 82 Bibliography 83 List of Figures 1.1 Gantt diagram . .6 2.1 Satellite size comparison . .9 2.2 Number of nanosatellites by announced launch year . 11 2.3 Nano/Micro-Satellite Trends by Purpose . 12 2.4 Keplerian elements . 13 2.5 Different orbits by altitude. 15 2.6 Computer generated image of objects in Earth orbit currently being tracked 16 3.1 Kepler's first law . 21 3.2 Kepler's second law . 21 3.3 ERBS Ground track for one day . 23 3.4 Meteor-3-07 Ground track for a period . 24 3.5 Equat. orbital shift fer period Meteor-3-07, 3D view . 24 3.6 Earth-centred fixed and Earth-centred inertial reference frames . 25 3.7 Azimuth, elevation and horizon plane . 26 3.8 A figure . 27 3.9 Another figure . 27 3.10 TLE Line 1 . 28 3.11 TLE Line 2 . 29 3.12 Ground station - Satellite basic geometry . 32 3.13 Earth coverage by a satellite at altitude H . 34 3.14 Intersection of the ground station latitude with different satellites . 35 3.15 Spherica39:online . 35 3.16 Spherical triangle A - SPP - B . 36 3.17 Satellite geometry duration visibility windor at location GS . 37 3.18 Spherical triangle GS - N - M . 38 3.19 Satellite's tangential velocity in the ECI frame . 39 3.20 Ground station - Satellite geometry . 42 viii ix 3.21 Doppler frequency shift of a Iridium satellite with a carrier frequency fc = 1:618GHz .................................... 44 3.22 Excel table to collect satellites information . 46 3.23 Excel table to collect ground station information . 46 3.24 Ground track without Earth's rotation . 51 3.25 Ground track with Earth's rotation . 51 3.26 Ground track after the first step of the longitude correction . 52 3.27 Ground track for one satellite . 52 3.28 Data in vectors moved to matrix . 53 3.29 Spherical-Cartesian coordinates . 54 3.30 Satellite ground track, 10 orbits. Ground station situated in Catalunya . 56 3.31 Satellite memory status while simulating the scenario of Figure 3.30 . 56 3.32 Code flow diagram . 57 4.1 Mission diagram flow . 58 4.2 Types of communication link . 61 4.3 BPSK modulation technique . 62 4.4 Natural sources of radio noise on the downlink of a space communications. 63 4.5 Bit Error Probability as a function of Eb=No ................. 64 4.6 Radio frequencies . 65 5.1 Satellite's ground track, H=404 km, i=51; 64◦ and Epoch year=2017, Epoch=346◦ 68 5.2 Satellite's memory status, H=404 km, i=51; 64◦ and Epoch year=2017, Epoch=346◦ ................................... 69 5.3 Satellite's ground track and memory status graphs, H=404 km, i=51; 64◦ and Epoch year=2008, Epoch=5◦ ....................... 70 5.4 Satellite's ground track H=3.500 km, i=51; 64◦ and Epoch year=2017, Epoch=346◦ 70 5.5 Satellite's memory status, H=3.500 km, i=51; 64◦ and Epoch year=2017, Epoch=346◦, Epoch=5◦ ............................. 71 5.6 Visibility window time - Altitude, ISS orbit . 72 5.7 Design data rate - Altitude, ISS orbit . 72 5.8 Satellite's ground track, H=404 km, i=90◦ and Epoch year=2017, Epoch=346◦ 73 5.9 Satellite's memory status, H=3.500 km, i=90◦ and Epoch year=2017, Epoch=346◦, Epoch=5◦ .................................... 73 5.10 Visibility window time - Altitude, SSO orbit . 74 5.11 Design data rate - Altitude, SSO orbit . 74 5.12 Qbapp Ground track . 76 5.13 Figure 5.12 and Figure 5.1 overlay . 76 x 5.14 Qbapp satellite memory status . 77 xi List of Tables 1.1 Interdependency relationship among tasks . .4 2.1 Satellite mass classification . .9 2.2 Orbits: Altitude classification . 14 3.1 ERBS details . 23 3.2 Meteor-3-07 details . 23 3.3 Parameters of the first TLE line . 28 3.4 Parameters of the second TLE line . 29 xii List of abbreviations BER Bit error rate BPSK Binary phase shift keying C Centre of the Earth ECF or ECEF Earth-centred fixed reference frame ECI Earth-centred inertial reference frame EO Earth Observation ESA European Space Agency FSK Frequency shift keying GEO Geosynchronous Orbit GMST Greenwich mean sideral time GS Ground station HEO High Earth Orbit HP Horizontal plane IRP International reference pole IRM International reference meridian ISS International Space Station ITU International Telecommunications Union JD Julian Date LEO Low Earth Orbit MEO Medium Earth Orbit RJD Reduced Julian Date RTS Rise time satellite SAT Satellite SSP Subsatellite point STS Set time satellite TLE Two line elements TT&C Tracking Telemetry & Command UT0 Universal time UT1 Standard universal time UTC Coordinated Universal time VLEO Very Low Earth Orbit VWT Visibility windows time WARC World Administrative Radio Conference xiii List of symbols a Semi-major axis Az Azimuth angle d Slant range Eb Energy received per bit e Eccentricity H Satellite altitude i Inclination angle No Noise spectral density r Radius of satellite'sorbit rE Radius of the Earth v True anomaly ta Satellite's rise time tb Satellite's set time tm Time when elevation angle is maximum xm Satellite's position when elevation angle is maximum γ Central angle γc Central angle for minimum elevation angle θ Elevation angle θc Elevation angle for minimum angle of elevation λ0 Initial position's longitude λs Latitude of subsatellite point λgs longitude of ground station τ Visibility window duration φ0 Initial position's latitude φgs Latitude of ground station φs Latitude of subsatellite point Ω Right ascension (or longitude) of the ascending node ! Argument of periapsis !E Angular velocity of Earth's rotation ECF frame !F Angular velocity of satellite in ECF frame !I Angular velocity of satellite in ECI frame Chapter 1 Introduction 1.1 Aim The aim of this study is to analyse the problem of the reduced windows communication between Very Low Earth Orbit (VLEO) and Low Earth Orbit (LEO) satellites and ground stations.